1. Field of the Invention
The present invention relates to an optical system and an optical apparatus having the same, which is suitable for an optical apparatus, such as a silver halide camera, a digital still camera, and a digital video camera.
2. Description of the Related Art
In the related art, as an image taking optical system having the long focal length, there is known an image taking optical system of a telescopic type that has a first lens unit having positive refractive power and a second lens unit having negative refractive power, in which the first lens unit and the second lens unit are provided in order from the object side to the image side.
In a telescopic lens, as the focal length increases, chromatic aberrations, such as a longitudinal chromatic aberration and a lateral chromatic aberration, among various aberrations, are more greatly generated. In general, in order to correct the chromatic aberrations, it is needed to increase both of the entire lens length and the effective diameter of a front unit. For this reason, a challenge of the telescopic lens is to successfully combine high optical performance with portability or convenience at the time of taking an image.
In Japanese Patent Application Laid-Open No. 2008-145584 and U.S. Pat. No. 6,239,919, a positive lens that is formed of a low dispersion material, such as fluorite, having anomalous partial dispersion, is disposed on the front side of a first lens unit where the incident height of an on-axis ray and the incident height of an off-axis principal ray increase to achieve correction of chromatic aberrations and miniaturization of an entire system. In U.S. Pat. No. 7,538,957, a negative lens that is formed of anomalous partial dispersion glass of a low refractive index and low dispersion is disposed on the image surface side of a rear unit where the incident height of an off-axis principal ray is large to achieve correction of chromatic aberrations and miniaturization of an entire system.
In recent years, in a large number of optical apparatuses, an image taking optical system of a telescopic type that satisfactorily corrects various aberrations including a chromatic aberration, is lightweight and compact as a whole and has high optical performance is required.